This invention relates to a process for stopping and starting an open-end friction spinning unit having two friction rollers that are arranged next to one another to form a wedge-shaped gap serving as a yarn forming point or region. The friction rollers are drivable in the same rotational direction by a driving arrangement. A feeding and opening device is connected to drives for the feeding of single fibers to the wedge-shaped gap and a withdrawal device is connected to a drive for the withdrawal of the formed yarn in the longitudinal direction of the wedge-shaped gap. A suction device is connected to a vacuum source for holding the fibers and the forming yarn in the wedge-shaped gap and a wind-up device is connected to a drive for winding the formed yarn onto a spool. An auxiliary suction device is provided for holding a yarn end, which auxiliary suction device is connected with a vacuum source and is aimed against the withdrawal direction of the yarn at the area of the wedge-shaped gap.
An open-end friction spinning unit is disclosed in European Published Unexamined Application (EP-OS) No. 34 427 where, after a yarn breakage, a manual piecing process takes place. The stopping of the spinning unit does not take place in a specified sequence so that, after a stoppage, a starting must be carried out by means of a corresponding manual piecing at the spinning unit that is accelerated again to operational speed. During this piecing, the spool is lifted off the wind-up device so that its drive is interrupted. Then a yarn end is wound off and shortened to a predetermined length and is used for piecing. The length of the yarn end is such that it is sufficient for a return into the area of the mouth of a fiber feeding duct. By-passing the withdrawl device, the yarn end is led to a yarn withdrawal tube and is subsequently sucked into the spinning unit. The yarn end is sucked into the spinning unit by the suction device affecting the wedge-shaped gap. In the case of this open-end friction spinning unit, it is also provided that by manual operation a suction slot of the suction device can be closed gradually starting from the area beginning at the yarn withdrawal tube so that consequently the yarn end is sucked into the spinning unit with a decreasing suction slot. As an extension of the wedge-shaped gap, an auxiliary suction device is located on the side that is opposite the withdrawal device which has the purpose of holding the yarn end tautly when the suction slot is completely closed. The end of the yarn end is not sucked into the auxiliary suction device but is held in the area of the mouth of a fiber feeding duct, where it has to be held in such a way that in a stretched condition it is held at a distance from the wedge-shaped gap. By means of switching on the suction device while the suction slot is opened up again, the end of the yarn end is to place itself in a stretched position in the wedge-shaped gap. When the suction device is switched on again, the feeding is started, after which the yarn withdrawal is started by placing the spool on the wind-up device. Then the pieced yarn is again placed in the withdrawal device. This type of piecing is very time-consuming and also unreliable since the return of the yarn end cannot really be controlled. In particular, such a piecing can no longer be carried out economically when a large number of such open-end friction spinning units are to be combined to form a complete machine which, after a stoppage, must then be started again.
This invention is based on the objective of providing a process of the initially mentioned type by means of which the piecing can be facilitated in a minimal amount of time, this process also being suitable especially for large-scale piecing or start spinning in the case of a spinning machine consisting of a plurality of open-end friction spinning units.
This objective is achieved according to the invention by coordinating the stopping of the drives and the switching-off of the vacuum source of the suction device in such a way that the yarn end forming by means of interruption of the fiber feeding remains in the sphere of action of the auxiliary suction device into which it is sucked before a restarting.
In this manner, the stopping of the open-end friction spinning unit, or the stopping of a complete spinning machine consisting of a plurality of such open-end friction spinning units, takes place in such a controlled way that the yarn end takes up a controlled position. The yarn end will then be located either in a position where it is ready to be pieced or it can reach such a position automatically in a very simple way.
In a further development of the invention, it is provided that during the restarting, before the switching-on of the drive of the device for the feeding of the fibers, the yarn is cut in front of the yarn end that was formed during the stoppage, and that the piecing will then take place at the yarn end obtained by the cutting. Thus, the circumstance is taken into that the yarn end being formed by the switching-off of the feeding device, because of the occurring lack of fibers, in most cases is not suitable for a piecing process. The yarn is then returned so far and cut so that a yarn end is obtained that is suitable for a piecing process.
In a further development of the invention, it is provided that before the actual stoppage, the spinning unit is slowed down from its operational speed to a lower speed, where the drives are coordinated in such a way that an unchanged yarn count is spun at the reduced withdrawal speed. The open-end friction spinning takes place at very high speeds, especially at a high withdrawal speed for the yarn. In order to eliminate the disadvantage that at such high speeds a controlled positioning of the yarn end resulting from the interruption of the spinning process is extremely difficult, the open-end friction spinning unit and correspondingly, the whole spinning machine is slowed down to a lower speed, especially to a lower withdrawal speed so that the controlled stoppage and especially the controlled receiving of the yarn end are facilitated. In this case, the realization is utilized that it is possible in open-end friction spinning to reduce the operating speeds and still obtain a yarn of the same yarn count.
In a further development of the invention, it is provided that during the restarting, the drives are first accelerated to a speed that is lower than the operational speed and at which the piecing takes place, where the lower speed of the drives is coordinated in such a way that the same yarn count is spun that is spun at the operational speed after which the drives are accelerated to operational speed. In this manner, longer time periods are made available in which the individual steps of the piecing process take place so that the reliability of the piecing and the quality of the pieced points is increased.
In a further development of the invention, it is provided that the drives of the withdrawal device and of the wind-up device are reversed for returning the yarn end into the auxiliary device. This may take place immediately after the stoppage or as the first step of the restarting process.
In a further development of the invention, it is provided that during the stoppage, a yarn reserve is produced between the rollers and the withdrawal device which is used up for the return of the yarn end into the auxiliary suction device. Although the production of the yarn reserve takes place during the stoppage, the using-up of the yarn reserve may take place either as the last step of the stoppage or as the first step of the restarting process.
In a further development of the invention, it is provided that the drive of the rollers and/or the connection of the suction device to its vacuum source are interrupted during the return. As a result, the return of the yarn end into the auxiliary suction device is not disturbed by the rollers or the suction device.
In a further development of the invention, it is provided that in the area of the auxiliary suction device, a yarn clamp is provided that closes after the return of the yarn end. As a result, it is achieved that the yarn end is held securely in the desired position without the requirement of outside energy for the holding. When the return and the clamping-in of the yarn end take place immediately after the stoppage, even extended periods of stoppage of the open-end friction spinning unit or of the spinning machine cannot result in a change of the position of the yarn end.
In a further development of the invention, it is provided that the yarn clamp is kept closed during the start of the rollers and after the switching-on of the drives of the withdrawal device and of the wind-up device at the time of the restarting process. By means of this measure, a cutting of the held yarn takes place automatically at a distance from the actual end since the yarn, because it is taken along via the rollers receives a false twist which at one point results in an opening of the spinning twist of the yarn and thus in a cutting of the yarn when the withdrawal device is switched on. This twisted end of the yarn has a shape that is especially suitable for piecing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.